Process for the treatment of plant materials in the preparation of fibers



Patented Mar. 17, 1931 UNITED STATES PATENT OFFICE DINSHAW RATTONJ'I NANJI, OF HEADINGLEY, LEEDS, ENGLAND, ASSIGNOR OF ONE- I HALF .TO DUNCAN MAYBURY STEWART, OF LONDON, ENGLAND PROCESS FOR THE TREATMENT OF PLANT MATERIALS IN THE PREPARATION OF FIBERS No Drawing. Application filed March 9, 1928, Serial No. 260,555, and in Great Britain April 29, 1927,

This invention comprises a new or improved process for separating the individual component fibers of fibrous plant tissues and like materials, and also for the product-ion directly from plant tissues of fibers suitable for spinning and for other purposes.

The fibers in the tissues of plants, such as for example flax, hemp, sisel, ramie and bamboo, are cemented together by pectinous, gummy and like substances.

Ordinarily, the fibers of flax and similar plants may be loosened" and separated by a fermentation process, technically known as retting, which results in the conversion of insoluble, pectinous, binding bodies into soluble pectin and itsderivatives which can be removed fromthe fibers by pressing and washing.

The retting process is open to objection on account of its being extremely lengthy to carry out, a period of treatment up to ten days being generally necessary. The process requires careful control and is particularly ,subject to the? deleterious eifect of adverse eather conditions. Again a full yield is never obtained, because of the considerable loss incurred in the scutching operations.

The yield is never more than 50% of the fiber content of the raw material. In order to overcome these disadvantages,-chemical r'etting or resolving processes, have been proposed, making use of such varied reagents as acids, benzine, carbon tetrachloride or" ethyl trichloride. Chemical processes on these lines have not, however, hitherto met with any marked degree of success. l

Processes using solutions of salt have also been proposed as an equivalent to retting. The following are examples of such proposals. In one case fibrous materials are treated with a resolving solution comprising a considerable proportion of resin used injconjunction with saponaceous ingredients such as alkali salts of fatty acids which render the resin soluble in water. In another case the fibrous materialis pickled in a solution of clear lime-water,- nitrate of soda, and oxalic acid. 7 In accordance with a further proposal the fibrous material is treated with a ten per cent solution of sodium aluininate under pressure, after which the stalks are treated also under pressure with carbon dioxide, so that aluminium hydroxide which is of considerable bulk is formed between the fibers and pushes them apart so that the individual fibers are easily separable.

The object of the present invention is an improved process for the treatment of the fibrous tissues, whereby the fibers are separated from. one another expeditiously, and the enveloping pectinous and like binding bodies are converted into a soluble and/or easily removable condition after a short time of treatment.

The improved process essentially consists in submitting the raw fibrous materials to the action of a chemical reagent, capable of the latter is capable of undergoing ionic ex change with the insoluble pectinous complexes to fullest advantage. It has been found after repeated experiment that ionic exchange in the true sense only takes place with neutral salts in very dilute solutions preferably under pressure. Even if the solution is very slightly alkaline or acidic the exchange of ions is impossible even such a weakly alkaline solution as soap inhibiting the reaction. Y

. Not only does the use of the neutral salts lead to no deterioration of the fibers even when the process is carried out at compara tively high pressures, but it will be observed that the anions of these compounds form sparingly soluble combinations with the alkamore certain the efliciency of the ionic exchange in accordance with the accepted physico-chemical theory of mass-action.

The depectinizing process in accordance with the present invention also serves as the basis of a new or improved process of treating ramie and like fibrous plant tissues for the production of fibers suitable for spin ning.

Although ramie is one of the strongest and finest of natural fibers known, it has hitherto not been possible to prepare the fiber economically, owing to theditficulties met with in, its isolation. Ramie grass con v tains an excessive amount of pectic substances and gums, which are very difficult to remove by the ordinary retting processes without deteriorating the quality of the fiber.

Further, in order to carry out the retting or mechanical processes, it is desirable that the grass should be treated in a comparative- .ly fresh condition, as the pectic and gummy substances binding the fibers harden as the grasses dry, and ofier greater difficulty to separation. Also, the ribbons of grass have to be separated mechanically from the stalk to produce a fiber of superior spinning quality directly from the ramie or like tissues, effecting considerable economies in labor and time, and obtaining a greatly improved yield of fiber.

After a preliminary depectinizing of the tissue. by means of a reagent capable of undergoing ionic exchange with the insoluble pectinous complexes and gums which are rendered soluble and rapidly removed thereby, the tissue is heated with a caustic alkaline solution under pressures much higher than hitherto employed in alkali treatments, namely about six to ten atmospheres, for a short time, for example, twenty to sixty minutes; or the heating may be carried out at temperatures corresponding to high vapor pressures of this magnitude.

This additional step is rendered necessary in the cases of ramie and allied fibers owing to the presence of substances, such as fats, waxes, cutaneous substances and resins, impregnating or adhering to the fibers.

The ramie tissue also contains coloring matternotably chlorophylwhich persists even after the above alkali treatment; so that I, prefer to bleach the fibers in any suitable and known manner subsequent to that treatment. The previous processes for depectin izifig, and purification under high pressure with alkali, facilitate bleaching processes, and

give 'a product which does not require any mechanical separation; as the ultimate fibers are directly'obtained. I may in some circumstances repeat the alkaline treatment of the fibers after bleaching; but in that case the duration of treatment may be shorter.

I am aware that the availability of an alkaline reagent in the treatment of fibers has been known; but, if such a reagent is employed before depectinizing, the result is 'to produce dark colored substances and impurities which are absorbed by the fibers or are deposited between them. Such impurities militate against bleaching, as they form insoluble substances necessitating'a more severe bleaching treatment, and giving a poor appearance to the bleached fiber. I

The process as outlined for the treatment of ramie requires a slight modification when applied to the treatment of such fibrous materialsas bamboo with aview to its utilization for the production of useful fibers capable of being spun and employed for ropes, sackingyand a number of other purposes.

I have found that bamboo is'not amenable to treatment by the full process as its fibers are rendered brittle and short if subjected to the full alkaline treatment. But if the tissues are depectinized and then submitted to caustic alkali treatment, e. g., in an autoclave until the pressure rises to from seven to ten atmosphere at which it may remain under treatment for a very short time, the individual fibers are found to be separated one from the other quite satisfactorily, and, at the same time, owing to the lignified tissue connecting plied in practice, giving typical working; 0011-. I r

ditions of temperature, pressure, and time of treatment.

A preliminary example gives details of the application of the invention to flax straw. Unretted flax straw is heated with a suitable quantity of 0.1 to 0.5 per cent of ammonium sulphate solution under a pressure of 1 to 2 atmospheres, or at temperatures corresponding to vapor pressures of this magnitude, for a period of from 60 down to 20 minutes.

, During this time the insoluble pectose which binds the fiber together is converted to soluble pectin without the fiber being deleteriously affected, and upon the completion. of

' this operation pressure is applied to the fiber In this way a very considerable saving in time is efiected, leading to a consequential diminution in the cost of producin the flax.

The reagent is preferably emp oyed for treating several batches of raw material, and can be used until its color becomes too dark and staining of the fiber occurs. Natural acids derived from the materials are liberated during treatment and are found to have a (flavorf'lable effect on the quality of fiber prouce After becoming valueless for further usein the process, the waste liquors, consisting in the above example of dilute solutions of ammonium sulphate, are available for ma nuring purposes.

As a working example of the process, as applied to the treatment of ramie and like grasses, the following is typical.

The unretted straw or grass may be heated with a suitable volume of 0.1 to 0.5 per cent ammonium sulphate solution at a pressure of 1 to 2 atmospheres or at. corresponding temperature for a period of time of from between sixty and twenty minutes. This treatment of the ramie results in the conversion of theinsoluble pectose substances into soluble pectin.

When this conversion of the pectose substances into the soluble pectinhas been ef fected, the fibrous mass is removed and pressed to eliminate the slimy matter adhering to the fibers.

- The unworked fibers are placed in an autoclave and heated with a solution of 24% caustic soda at a pressure of from 6 to 10 atmospheres or thereabouts for a period of between twenty and sixty minutes. At the expiration of the required time the fibers are removed from the autoclave and washed and dried, the resultant product being found to have a lustrous silky appearance and texture, the appearance being comparable to that of the lustrous cellulose products known to com merce'as artificial silk; but in addition the material prepared in accordance with this invention is of a much greater tensile strength than the filaments of the products known as artificial silk. Furthermore, the lustrous material can be produced at a relatively low cost, compared with ordinary artificial silk, since abundant and cheap suppliesxof ramie are available and the plant can be extensivelycultivated.

present used is first cut to convenient length and thickness, and heated as previously set forth,

preferably with very dilute solutions of neutral salts or the alkali metals or ammonium. 0.1 to 0.5% ammonium sulphate may conveniently be employed at a pressure of from 1 to 2 atmospheres or at temperatures corresponding to vapor pressures of this magnitude for a period of time between sixty and twenty minutes. This treatment separates the individual fibers. In order to render these fibers pliable and suitable for spinning, the fats, waxes, cutaneous substances and res ins contained therein are removed'or destroyed by heating with alkaline solution, conveniently 24% caustic soda solution, in an autoclave until the pressure rises to from seven to ten atihos heres. When the pressure has reached t is point, it is lowered again to normal, and the process is complete. The maximum pressure must not be maintained for any considerable period, and in large scale practice, wherein say a ton of material is treated at a time, the period of treatment can be extended to as much as fifteen minutes or more. This special treatment with alkali has been found necessary on account ofthe fact that prolonged treatment bamboo fiber over those such as hemp, jute;

and the like previously used for rope and sack manufacture.

I have found that the outer layer or skin of the bamboo cane is not susceptible to the above treatment, owing to its constitution being entirely diiferent from that of the enclosed fibrous material. When the mass has, however, undergone the alkali treatment and whilst it is still moist, this husk or skin is softened and may be readily detached from the fiber and removed.

If the mass is allowed to dry before this removal, the husk is hardened and difliculty is experienced owing to thetenacity with which adjacent fibers are held to it.

Owing to the color of the bamboo fiber and the uses to which it is likely to be subjected, there is little necessity for any bleachmg process subsequent to the alkali treatment. If desired, however, the fiber may be bleached in known manner although this may occasion mechanical weakening.

I claim:

1; A process whereby fibrous plant tissue is heated with a suitable quantity of 0.1 to

0.5per cent ammonium sulphate solution at a temperature corresponding to a vapor pressure of-from 1 to 2 atmospheres for a period of from 60' down to minutes, completion of-which operation pressure is applied to the mass to remove the slimy mat- .ter, and subsequentlyethe fiber is washed.

the depectinized tissue with a caustic alkaline solution at temperatures corresponding to high vapor pressures of fromG to 10 atmospheres. P

3. A process of fiber .production from fibrous plant tissues by acting upon the tissue with an aqueous solution of a neutral salt; of a strong base having a concentration up to 0.5 per cent and subsequently heating the depectinized tissue with a 24% solution of caustic soda ata temperature corresponding to a"vapor pressure of from 6 to 10 atmospheres. N

4. A process of fiber production (from fibrous plant tissues in which the unretted straw or grasses are heated with a suitable volume of 0.1 to 0.5 per cent ammonium sulphate solution at a pressure of from 1 to 2 atmospheres for aperiod of-time of from between 60 and 20 minutes, the fibrous mass is pressed to remove the slimy matter ad- V vapor pressure of from 6 to 10 atmospheres for a period of time between 20 and 60 minutes.

5. A process of treating fibrous materials for the production of fiber in which the raw material is treated with a very dilute solution of a neutral salt of a strong base. and subsequently the depectinized fibers are heated with caustic alkaline solution in a closed Vessel until the pressure rises to from 7v to 10 atmospheres, andhaving attained this magnitude is lowered again to normal. V 6. A process of. treating fibrous material 56 for the production of fiber in which the raw materialis heatedwith a very dilute solution of a neutral salt of a strong base, asfor ex ample, a 0.1 to'.0.5 per cent solution of ammonium sulphatev at a temperature corre- I component' fibers of plant tissues by heating the raw material with a solution of a neutral after the salt of ammonium having a concentration up to 0.5 per cent. 7

8. A process for separating the individual component fibers of plant tissues by heating the raw material with an aqueous solution of a neutral salt of ammonium having a concentration up to 0.5 per cent.

9. A process for separatlng the individual component fibers of plant tissues by heating the raw material with a. 0.1 to 0.5 per cent aqueous solution ofa neutral salt of ammonium, the salt being one whose union is capable of precipitating metals of the alkaline earth mospheres, and afterwards bleaching the fibers to'remove the discoloration due to matt ers such as chlorophyl present in the tissues.

11. A process of .treating fibrous material for the production of fiber in which the raw material is heated with a very dilute solution of a neutral salt of a strong base, as for example, a 0. 1 to 0.5 per cent solution of ammonium sulphate at a temperature corresponding to a vapor pressure of from 1 to 2 atmospheres for a period of time between sixty and twentyminute's, and subsequently the depectinized fibers are heated with a 24% caustic'soda solution in an autoclave until the pressure rises to from 7 to 10 atmospheres and having reached this point is lowered again to normal, after which, while themass is still moist, the husk or skin in its softened condition is detached from the fiber and removed. x

In testimony whereof I afiix my signature.

DINSHAVV RATTONJI NANJ I. 

